12,806 research outputs found
The Mass of the Centaurus A Group of Galaxies
The mass M, and the radius R_h, of the Centaurus A group are estimated from
the positions and radial velocities of 30 probable cluster members. For an
assumed distance of 3.9 Mpc it is found that R_h \sim 640 kpc. The velocity
dispersion in the Cen A group is 114 \pm 21 km/s. From this value, and R_h =
640 kpc, the virial theorem yields a total mass of 1.4 \times 10^{13} M_{\sun}
for the Cen A group. The projected mass method gives a mass of 1.8 \times
10^{13} M_{\sun}. These values suggest that the Cen A group is about seven
times as massive as the Local Group. The Cen A mass-to-light ratio is found to
be M/L_B = 155-200 in solar units. The cluster has a zero-velocity radius R_0 =
2.3 Mpc.Comment: 8 pages, 1 figure, in LaTeX format; to appear in the Astronomical
Journal in January 200
Are the Luminosities of RR Lyrae Stars Affected by Second Parameter Effects?
There is a serious discrepancy between the distance to the LMC derived from
the Cepheid Period-Luminosity relation and that obtained by using the Galactic
calibration for the luminosity of RR Lyrae stars. It is suggested that this
problem might be due to the fact that second parameter effects make it
inappropriate to apply Galactic calibrations to RR Lyrae variables in the
Magellanic Clouds, i.e. Mv(RR) could depend on both [Fe/H] and on one or more
second parameters.Comment: 10 pages as uuencoded compressed Postscript. Also available at
http://www.dao.nrc.ca/DAO/SCIENCE/science.htm
What are S0 (0) Galaxies?
Among early-type galaxies with almost circular isophotes E0 and E1 galaxies
are, at 99.3% significance, more luminous than face-on objects classified as S0
(0) and S(0) (1). This result supports the view that rotation and "diskiness"
are more important in the outer regions of faint-early type galaxies than they
are for more luminous galaxies of very early morphological type.Comment: 7 pages. 0 figures. Astrophysical Jounral Letters in pres
The Future of Extragalactic Research
It is argued that the astronomy of the twenty-first century will be dominated
by computer-based manipulation of huge homogeneous surveys of various types of
astronomical objects. Furthermore combination of all observations with large
telescopes into a single database will allow data mining on an unprecedented
scale.Comment: Millennium Essay to be published in Vol. 119 of the Publications of
the Astronomical Society of the Pacific, replaced with a LaTeX version (4
pages
Hypersurface homogeneous Killing spinor space-times
I present a complete list of hypersurface homogeneous space-times admitting a
non-null valence two Killing spinor, including a new class admitting only
exceptional Killing tensors. A connection is established with the
classification of locally rotationally symmetric or boost symmetric
space-times.Comment: 16 page
A Comparison Between the Globular Clusters in NGC 5128 and the Galaxy
Some of the properties of the globular clusters in NGC 5128 are compared to
those of Galactic globular clusters. Assuming the color- metallicity relations
that hold for Galactic globular clusters then the metal-poor clusters in NGC
5128 that have [Fe/H] < -1.80 are significantly fainter than are the more
metal-rich globulars in that galaxy. No such metallicity dependent luminosity
difference is observed among the globular clusters associated with the Milky
Way. Furthermore the NGC 5128 cluster sample contains two objects that, on the
basis of their observed colors, appear to be super metal-poor. It is speculated
that many of these apparently faint and metal-poor clusters in NGC 5128 are
actually objects resembling intermediate-age Galactic open clusters. It is also
found that large clusters with FWHM > 10 pc are typically less luminous in NGC
5128 than are their more more compact counterparts. In this respect the NGC
5128 cluster system is similar to the Galactic globular cluster system.
Finally, the present data may hint at the possibility that the NGC 5128 cluster
system differs from that surrounding the Milky Way, in that the NGC 5128
objects do not seem to exhibit a clear cut gap between the regions of the FWHM
vs M_v plane that are occupied by globular clusters and dwarf spheroidal
galaxies.Comment: To be published in the Astronomical Journa
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